Infrared source utilizing an exothermic chemical charge having stable and nonsegregating reaction products

ABSTRACT

A radiant energy source is described comprising a crucible formed of a refractory material and containing an exothermic charge, the reaction products of which form a stable, nonsegregating matrix preventing large scale separation of the reaction products, thereby permitting the energy source to be mounted in a wide variety of attitudes. Cylindrical heat shields of varying lengths may be provided around the crucible permitting a variety of radiation patterns to be achieved, from a very narrow radiation cone up to slightly less than omnidirectional pattern. A valve is provided within the crucible for venting gases generated by the charge while sealing within the crucible any solid or liquid products of the reaction. A liner is disposed between the exothermic charge and the inner wall of the crucible for sealing the crucible wall against leakage of reaction products, thereby preventing deposits which would otherwise reduce the emissivity of the crucible wall.

United States Patent [72] Inventors Raymond W. Thomas Phoenix; I Abraham L. Pittinger, Scottsdale, Ariz.

[21 Appl. No. 803,587

[22] Filed Mar. 3, 1969 [45] Patented May 18, 1971 [73] Assignee Talley Industries, Inc.

Mesa, Ariz.

[54] INFRARED SOURCE UTILIZING AN EXOTHERMIC CHEMICAL CHARGE HAVING STABLE AND NONSEGREGATING REACTION PRODUCTS 13 Claims, 3 Drawing Figs.

[52] US. Cl 250/85,

[51] Int. Cl HOIj 35/00 [50] Field of Search 102/31,

[56] References Cited UNITED STATES PATENTS 2,933,317 4/1960 Pittinger et al. 250/85X ABSTRACT: A radiant energy source is described comprising a crucible formed of a refractory material and containing an exothermic charge, the reaction products of which form a stable, nonsegregating matrix preventing large scale separation of the reaction products, thereby permitting the energy source to be mounted in a wide variety of attitudes. Cylindrical heat shields of varying lengths may be provided around the crucible permitting a variety of radiation patterns to be achieved, from a very narrow radiation cone up to slightly less than omnidirectional pattern. A valve is provided within the crucible for venting gases generated by the charge while sealing within the crucible any solid or liquid products of the reaction. A liner is disposed between the exothermic charge and the inner wall of the crucible for sealing the crucible wall against leakage of reaction products, thereby preventing deposits which would otherwise reduce the emissivity of the crucible wall.

ZSheets-Sheet 1 FIG. 1

INVENTORS RAYMOND W. THOMAS ABRAHAM L.PITTINGER BY j film, 641w, haw raw.

ATTORNEYS Patented May 18, 1971 3,578,974

2 Sheets-Sheet INVENTORS RAYMOND W. THOMAS ABRAHAM L. FITTING ER ATTORNEYS INFRARED SOURCE UTILIZING AN EXOTIIERMIC CHEMICAL CHARGE HAVING STABLE AND- NONSEGREGATING REACTION PRODUCTS BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to a source of radiant energy, primarily in the infrared region, in which an exothermic chemical charge is used to generate high temperatures in a crucible, which crucible acts as a black body radiator. Energy sources of this type are particularly useful as targets for gunnery practice with missiles capable of homing on a source of infrared radiation. Mounted on target drones, aircraft, rockets, balloons or the like, they may be sent aloft and, when ignited, attract missiles aimed at the vehicles which carry them in the same manner as such missiles would be attracted to comparable infrared sources such as jet and rocket engines.

2. History of the Prior Art Radiant energy sources of the type described above (sometimes referred to as infrared augmentors) have been in use since the 1950's primarily for military applications. Two such energy sources are described in US. Pat Nos. 2,933,317, issued Apr. l9, I960, and 3,219,827, issued Nov. 23, 1965. Both of these patents describe infrared sources, and refer to problems encountered with respect to such sources, for example, achieving high emissivities, obtaining various types of radiation patterns, and permitting mounting of thecrucible in various attitudes. In the first mentioned patent, aluminum and iron oxide are reacted to form a pool of molten iron topped by a layer of slag. This type of radiation source must be so oriented, when mounted, so that the molten pool formed during the reaction remains in contact with the radiating surface of the crucible. Ignitionof the exothermic reaction in such devices is achieved electrically, necessitating electrical wires which necessarily must pass through the crucible wall at some point. Ordinarily, the crucible must be oriented so that this point does not fall within the pool of molten iron since the insulation would be destroyed and the molten iron permitted to escape from the crucible. If the amount of exothennic charge is kept small so that the reaction occurs only for a few seconds, leakage of molten reaction products can be tolerated under certain conditions. However, when an energy output lasting longer than a few seconds is desired, as is most often the case, the mounting orientation of the energy source must assure that the electrical connections through the crucible wall do not fall within the melt formed by the reaction.

Further, in radiant energy sources of generating a sustained output, the radiating surface is limited to that portion of the crucible in contact with the molten reaction products This has seriously limited the radiation pattern obtainable in previously known infrared sources.

Additionally, at the reaction temperatures of several thousand degrees centigrade ordinarily produced in known infrared sources, the radiating wall of the crucible, commonly formed of graphite, becomes pitted and therefore permeable to gases evolved in the chemical reaction, if it is too thin. However, when the radiating crucible wall is made thick enough to prevent such leakage and/or diffusion, it unduly limits the thermal output of the unit. Were some leakage of magnesium vapor, for example, to be tolerated, the resulting oxide would spread over the exterior black radiating surface of the crucible, coating it and therefore reducing its efficiency as a black body radiator. It is possible to insert a solid liner between the chemical charge and the adjacent crucible wall, and although this can be effective in sealing in the reaction products, it absorbs some of the reaction energy, lowering the efficiency of the crucible as a radiator.

SUMMARY OF THE INVENTION In accordance with the invention, a radiant energy source is provided in which the exothermic charge contained in the radiating crucible utilizes constituents which react to form a stable, nonsegregating matrix, preventing large scale separation of the reaction products, such as occurs in previously known devices to form the molten pool of iron described above. In this manner the radiating surface of the crucible is that portion of the crucible in contact with the entire exothermic charge, which portion remains substantially the same throughout the reaction. The radiating portion of the crucible wall may thus be predetermined, and is unaffected by the mounting orientation of the crucible. Reaction gases are permitted to escape from the crucible substantially independently of its mounting orientation by the provision of a closure structure incorporating a valve which seals off the crucible to prevent the escape of minor quantities of molten and solid reaction products over a wide variety of mounting orientations, while venting the gaseous reaction products from the crucible.

In particular, a highly exothermic reactive charge which reacts to form a stable matrix of the type described above may be formed of a stoichiometric mixture of an oxide of an element from the fourth period of Group VIII of the Periodic Table (i.e. iron, nickel or cobalt oxide), and an element from the third period of Group [IA of the Periodic Table (i.e., magnesium). A stoichiometric mixture of Fe 0 and Mg. is particularly satisfactory, and reacts as follows:

Preferably, the constituents are formed of finely divided powders (e.g. about 200 mesh) and are well mixed and compacted under a few thousand pounds pressure to form a dimensionally stable charge shaped to conform to the inner wall of the cruci ble. This makes the charge easy to handle and promotes combustion.

In order to prevent leakage of gaseous and molten reaction products through the crucible radiating wall, a liner is provided between the charge and the adjacent wall, which liner is formed of a mixture of finely divided exothermically reactive constituents capable of forming a barrier against such leakage and of oxidizing the reaction products which come in contact with it; at the same time, the liner constituents react exothermically to add to, rather than detract from, the overall thermal efficiency of the device.

In a preferred embodiment of the device, in which the crucible is in the form of a cylinder, an exterior cylindrical shield thermally insulated from the crucible wall, may be provided so that the extent to which the shield covers the crucible wall determines the radiation pattern of the device. By this means, the radiation pattern may be varied from a narrow cone up to almost an omnidirectional pattern.

DESCRIPTION OF THE DRAWINGS Particular embodiments of the invention will be described below in conjunction with the accompanying drawings, in which:

FIG. I is a partial sectional view of an embodiment of the invention;

FIG. 2 is a detail sectional view of the embodiment of FIG. 1 showing the closure assembly; and

FIG. 3 is a side elevation, partially broken away, of the embodiment of FIG. 1 with a different length heat shield to achieve a narrower radiator pattern.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the invention shown in FIG. 1 is especially suited to manufacture by conventional techniques and is easily adapted to a wide variety of radiation patterns. A cylindrical crucible body 1 formed of graphite (sometimes called electrographite) is provided, one end of which is open and the other end of which is hemispherically shaped. Any other suitable refractory material may be used which can provide the required surface emissivity and will withstand the temperatures generated during the reaction (on the order of several thousand degrees Centigrade). The crucible wall thickness affects the thermal efficiency of the device and its radiation temperature rise time.

Wall thicknesses of about between 0.190 inch and 0.500 inch have been satisfactorily used. The wall must be thick enough to retain its structural integrity during the reaction, which lasts for about 15 to 20 seconds, despite pitting of its interior surface by the reaction. The wall of crucible body 1 in this embodiment is 0.200 inch thick.

A chemical charge 2, formed of a mixture of finely divided Fe 0, and Mg which has been compacted at about 22,000 p.s.i., is placed in the crucible so that its exterior wall conforms to the crucible wall.

When formed, a hollow space is left in the interior of the charge for an igniter 3, the electrical actuating wires 4 of which extend through a hollow tube 5 formed in the charge.

Chemical charge 2 is about one-eighth inch smaller in diameter than the interior of the crucible, to allow for liner 6 between the charge and the adjacent crucible wall. A wire washer 7 may conveniently be placed in the crucible before the charge is inserted, thus providing a space about the charge within which liner 7 may be formed.

Liner 6 is a loosely compacted mixture of finely divided exothermically reactive constituents present in nonstoichiometric proportions; an excess of oxide is present in order to oxidize any small droplets (i.e. on the order of one thirty-second inch) of, say, molten magnesium or vapor thereof fonned during the reaction of the main charge thereby preventing leakage through the crucible wall, which is permeable during the peak of the reaction. As explained above, metal vapors, if permitted to diffuse through the crucible wall, would lightly coat the exterior radiating wall of the crucible and reduce its emissivity.

1n the embodiment of FIG. 1, the liner is an intimate mixture of Fe t) and Aluminum in the ratio 83 percent to 17 percent by weight. (All proportions herein are by weight, unless otherwise stated). A stoichiometric mixture would be about 76 percent-24 percent.

The liner mixture may be poured into the space left between the charge 2 and the crucible. Subsequent vibration of the crucible compacts the liner materials sufficiently and the liner is then retained in place by a washer 8 formed of asbestos cord which may be set into a depression 9 formed in the periptery of the outer end of the charge. Retention of washer 8 is aided by annular ring 10, which is made of an inert material such as marimite or plasterboard so that it decomposes upon ignition of the charge, thereby freeing the adjacent flapper valve 11.

Also forming part of the crucible is a closure assembly provided on the open end of the crucible body, which includes a refractory closure disc 12 which seats into the crucible body 1, having a plurality of vent holes (vents) l3 distributed circumferentially about its surface, for providing communication between the interior and exterior of the crucible. The interior surface of closure disc 12 is convexly shaped to cooperate with the adjacent concavely shaped surface of flapper valve 1 1;

A cylindrical metal shield 14, preferably steel, is mounted exteriorly of the crucible, and abuts a shoulder 15 which pro vides a space between the shield and the radiating surface of the crucible. This space is filled with a high temperature insulating material such as a high temperature ceramic felt or air, to prevent radiation from the crucible surface so shielded. The shield is bonded to shoulder 15 by a high temperature ceramic mortar 16.

Referring to F 1G. 2, which more clearly illustrates the closure assembly, a series of sealing discs 17, 18, 19 and 20 is provided exteriorly of closure disc 12 for permitting the escape of gases from the crucible while preventing entry of moisture or other contaminates into the crucible before the device is used. Moisture, for example if, permitted to enter the crucible, would vaporize upon ignition of the charge and the device would effectively become a bomb.

Sealing discs 17 and 19 are one-eighth inch thick asbestos, and are separated by a heavy gauge wire screen 18 for facilitating gas transmission and absorbing heat from the gases. Sealing discs 17, 18 and 19 are followed by a thin (0.0015 in.) layer 21 of polyethylene or an equivalent material capable of forming a moisture barrier, which is ruptured by gas pressure upon actuation of the device, followed by a steel perforated closure cup 20 for holding the discs in place, which cup is fastened to shield 14. Asbestos discs 17 and 19 contain small (on the order of 0.020 in.) holes distributed over their surfaces to enhance their permeability.

An eyelet 22 extending through the centers of discs 17-2l carries a steel backup place 23 to cool the escaping gasses and to facilitate mounting. Mounting member 24 carries an electrical connector 26 for delivering ignition current to the device. An annular space 27 provided in the surface of closure disc 12 facilitates gas flow from vent holes 13 through the closure discs.

Ignition of the charge 2 requires a temperature of about 1500 to 1800 F. sustained for several seconds. In order to achieve this, an igniter 3 is provided which is formed ofa conventional electrically actuable squib capable of briefly generating about 800 F. surrounded by a compacted stoichiometric mixture of tungstic oxide (W0 and Aluminum powders, which reacts with sufficient heat to ignite the main charge. The wires 4 from igniter 3 are let through vent holes 13 in closure disc 12 and through eyelet 22 to connector 25.

Upon ignition of igniter 3, the main charge 2 is set off, heating the crucible wall to red heat, and also igniting the liner; washer 10 melts or breaks down, freeing flapper valve 11. When the device is mounted horizontally, as shown in FIG. 1, small quantities of solid and liquid reaction products which break away from the stable matrix formed by the main charge fall to the lower side of the crucible, independently of its angular orientation about its longitudinal horizontal axis, closing off the lower vent holes 13 and opening the opposite (upper) vent holes to permit reaction gases to escape. lt will be apparent that the crucible can be mounted in any of a wide variety of orientations, from vertical (radiating end down) through horizontal and even through a substantial angle above horizontal (i.e. the right end of the crucible higher than the left end in HQ 1).

FIG. 3 illustrates an embodiment of the invention similar to FlG. 1 except that shield 14 extends over a much greater length of the crucible resulting in a much narrower radiation pattern than the embodiment of HG. 1. By thus varying the length of the heat shield, radiation patterns may be achieved anywhere from a very narrow cone up to almost 360.

It will be apparent to those skilled in the art that modifications may be made in the above-described embodiments without departing from the scope and spirit of the invention, which is intended to be limited only in accordance with the following claims.

We claim:

1. An infrared radiation source comprising a crucible formed of a refractory material, an exothermic charge contained therein having as one constituent an oxide of an element from the fourth period of Group VIII of the Periodic Table and as another constituent, magnesium and means for igniting said exothermic charge so that it produces radiation from the exterior surface of said crucible, substantially all of the reaction products of the exothermic charge thereby forming a stable, nonsegregating matrix preventing large scale separation of said products.

2. An infrared radiation source as defined in claim 1 wherein said constituents are Fe 0 and Mg.

3. An infrared radiation source as defined in claim 1 including a liner disposed between the inner wall of said crucible and the exothermic charge, comprising a mixture of finely divided exothermically reactive coattituents, capable of forming a barrier against transmissior )f the reaction products of said exothermic charge, one of said reactive constituents being a metal oxide, said metal oxide being present in substantially greater than stoichiometric proportion whereby said liner constituents react upon ignition by the exothermic charge to contribute to the thermal output of said crucible and to oxidize any oxidizable reaction products of said charge coming in contact with the liner.

4. An infrared radiation source as defined in claim 3 wherein said reactive constituents are ferric oxide and aluminum.

5. An infrared radiation source as defined in claim 4 wherein said ferric oxide and aluminum comprise about 83 percent and 17 percent respectively of said liner constituents.

6. An infrared radiation source as defined in claim I, including a plurality of vents communicating between the interior and the exterior of said crucible distributed about a surface of the crucible, and a valve mounted within the crucible adjacent said vents, said valve being actuable by the expanding reacting constituents of the exothermic charge, during its reaction, to seal the vents on the lower portion of said surface sufficiently to preclude escape of reaction products therethrough and to uncover the vents on the upper portion of said surface for releasing gases generated during said reaction.

7. An infrared radiation source comprising a crucible formed of a refractory material, said crucible being substantially in the form of a cylinder having a closure assembly disposed at one end thereof; an exothermic charge contained therein having as one constituent an oxide of an element from the fourth period of group VII] of the Periodic Table and as another constituent, magnesium; and means for igniting said exothermic charge so that it produces radiation from the exterior surface of said crucible, substantially all of the reaction products of the exothermic charge thereby forming a stable, nonsegregating matrix preventing large scale separation of said products, said closure assembly comprising:

a refractory closure disc forming one end of said cylinder and having a plurality of vent holes distributed circumferentially about its surface;

a refractory valve element disposed interiorly of the closure disc, said closure disc and valve element having opposed surfaces facing each other, one of which is convex and the other of which is concave so that the valve element is movable to seal a portion of said vent holes while leaving an opposite portion of said vent holes open to transmit gases generated by the exothermic charge exteriorly of the crucible.

8. An infrared radiation source as defined in claim 7,

wherein said closure assembly includes a plurality of gas permeable discs disposed in series to permit the escape of gaseous reaction products exteriorly of the crucible 9. An infrared radiation source as defined in claim 8, wherein said closure assembly includes a thin, rupturable vapor-impermeable membrane for preventing moisture from entering the crucible prior to ignition of the exothermic charge.

10. An infrared radiation source comprising a cnicible formed of a refractory material, an exothermic charge contained therein consisting of constituents which chemically react with each other upon ignition of such charge such that substantially all of their solid reaction products form a stable, nonsegregating matrix preventing large scale separation of said products, and means for igniting said exothermic charge to produce radiation from the exterior surface of said crucible.

l I. An infrared radiation source as defined in claim 10, said radiation source including a plurality of vents communicating between the interior and the exterior of said crucible distributed about a surface of the crucible, and a valve mounted within the crucible adjacent said vents, said valve being actuable by the expanding reacting constituents of the exothermic charge, during its reaction, to seal the vents on the lower portion of said surface sufficiently to preclude escape of reaction products therethrough and to uncover the vents on the upper portion of said surface for releasing gases generated during said reaction.

12. In combination with an infrared radiation source including a crucible formed of a refractory material containing an exothermic charge and means for igniting said charge to produce thermal radiation from the surface of said crucible, the improvement comprising a liner disposed between the exothermic charge and the crucible wall for generating additional heat and preventing transmission of reaction products of the exothermic charge through the crucible wall, said liner comprising a mixture of finely divided exothermically reactive constituents capable of forming a barrier against transmission of said reaction products, one of said constituents being a metal oxide, said metal oxide being present in substantially greater than stoichiometric proportionto oxidize any such reaction products.

13. An infrared radiation source as defined in claim 12, wherein said reactive constituents are ferric oxide and aluminum, said ferric oxide and aluminum comprising about 83 percent and 17 percent respectively of said liner. 

2. An infrared radiation source as defined in claim 1 wherein said constituents are Fe304 and Mg.
 3. An infrared radiation source as defined in claim 1 including a liner disposed between the inner wall of said crucible and the exothermic charge, comprising a mixture of finely divided exothermically reactive constituents, capable of forming a barrier against transmission of the reaction products of said exothermic charge, one of said reactive constituents being a metal oxide, said metal oxide being present in substantially greater than stoichiometric proportion whereby said liner constituents react upon ignition by the exothermic charge to contribute to the thermal output of said crucible and to oxidize any oxidizable reaction products of said charge coming in contact with the liner.
 4. An infrared radiation source as defined in claim 3 wherein said reactive constituents are ferric oxide and aluminum.
 5. An infrared radiation source as defined in claim 4 wherein said ferric oxide and aluminum comprise about 83 percent and 17 percent respectively of said liner constituents.
 6. An infrared radiation source as defined in claim 1, including a plurality of vents communicating between the interior and the exterior of said crucible distributed about a surface of the crucible, and a valve mounted within the crucible adjacent said vents, said valve being actuable by the expanding reacting constituents of the exothermic charge, during its reaction, to seal the vents on the lower portion of said surface sufficiently to preclude escape of reaction products therethrough and to uncover the vents on the upper portion of said surface for releasing gases generated during said reaction.
 7. An infrared radiation source comprising a crucible formed of a refractory material, said crucible being substantially in the form of a cylinder having a closure assembly disposed at one end thereof; an exothermic charge contained therein having as one constituent an oxide of an element from the fourth period of group VIII of the Periodic Table and as another constituent, magnesium; and means for igniting said exothermic charge so that it produces radiation from the exterior surface of said crucible, substantially all of the reaction products of the exothermic charge thereby forming a stable, nonsegregating matrix preventing large scale separation of said products, said closure assembly comprising: a refractory closure disc forming one end of said cylinder and having a plurality of vent holes distributed circumferentially about its surface; a refractory valve element disposed interiorly of the closure disc, said closure disc and valve element having oppOsed surfaces facing each other, one of which is convex and the other of which is concave so that the valve element is movable to seal a portion of said vent holes while leaving an opposite portion of said vent holes open to transmit gases generated by the exothermic charge exteriorly of the crucible.
 8. An infrared radiation source as defined in claim 7, wherein said closure assembly includes a plurality of gas permeable discs disposed in series to permit the escape of gaseous reaction products exteriorly of the crucible.
 9. An infrared radiation source as defined in claim 8, wherein said closure assembly includes a thin, rupturable vapor-impermeable membrane for preventing moisture from entering the crucible prior to ignition of the exothermic charge.
 10. An infrared radiation source comprising a crucible formed of a refractory material, an exothermic charge contained therein consisting of constituents which chemically react with each other upon ignition of such charge such that substantially all of their solid reaction products form a stable, nonsegregating matrix preventing large scale separation of said products, and means for igniting said exothermic charge to produce radiation from the exterior surface of said crucible.
 11. An infrared radiation source as defined in claim 10, said radiation source including a plurality of vents communicating between the interior and the exterior of said crucible distributed about a surface of the crucible, and a valve mounted within the crucible adjacent said vents, said valve being actuable by the expanding reacting constituents of the exothermic charge, during its reaction, to seal the vents on the lower portion of said surface sufficiently to preclude escape of reaction products therethrough and to uncover the vents on the upper portion of said surface for releasing gases generated during said reaction.
 12. In combination with an infrared radiation source including a crucible formed of a refractory material containing an exothermic charge and means for igniting said charge to produce thermal radiation from the surface of said crucible, the improvement comprising a liner disposed between the exothermic charge and the crucible wall for generating additional heat and preventing transmission of reaction products of the exothermic charge through the crucible wall, said liner comprising a mixture of finely divided exothermically reactive constituents capable of forming a barrier against transmission of said reaction products, one of said constituents being a metal oxide, said metal oxide being present in substantially greater than stoichiometric proportion to oxidize any such reaction products.
 13. An infrared radiation source as defined in claim 12, wherein said reactive constituents are ferric oxide and aluminum, said ferric oxide and aluminum comprising about 83 percent and 17 percent respectively of said liner. 